Modern electronics typically consist of a collection of functional units such as gates, registers, flip flops, and arithmetic logic units. Data travels through the collection of functional units along a data path. The functional units are synchronized to a clock signal that travels through the collection of functional units on a clock path.
Radiation hardening is a method of designing electronic devices to make them resistant to malfunctions caused by ionizing radiation such as particle radiation and high-energy electromagnetic radiation. Ionizing radiation can cause what are known as single-event effects (SEEs), where charge might accumulate on a node of a circuit causing an incorrect state change, a short, or other such undesirable effect. One specific type of SEE is commonly referred to as a single-event transient (SET), which occurs when charge from ionization collects on a specific node of a circuit causing a temporary voltage change on the node. Ionizing radiation is present on the surface of the earth, in the presence of nuclear reactions for example, but becomes more prevalent at higher altitudes where planes fly, and becomes even more prevalent in outer space where satellites orbit.
One method of radiation hardening to an SET utilizes redundant data paths and/or redundant clock paths within a circuit, and implements voting circuits to discard disagreeing data. In the instances where not all data paths agree, however, the output drive of the voting circuit can be reduced. Additionally, sometimes ionizing radiation on an internal node of the voting circuit can cause the voting circuit itself to be adversely affected by the same type of SETs it is meant to protect against.